Acute respiratory infections (ARI) including influenza-like illness (ILI) can result in significant morbidity and mortality, direct medical expenses including outpatient visits and hospitalizations, and indirect costs due to lost work and school days. New population-based studies assessing the incidence and etiologies of ARI/ILI need to be conducted as ARI/ILI incidence and transmission as well as factors associated with ARI/ILI epidemiology have changed since previous population-based studies were conducted decades ago. Likewise, modern diagnostic techniques such as reverse transcription polymerase chain reaction (RT-PCR) expands the potential for greater knowledge regarding the epidemiology and etiology of viral ARI/ILIs; in previous historical studies in an estimated 75% of ARI/ILI-associate samples no virus was identified. Specific Aims: 1) Identify incidence of ARI and ILI in a representative population-based community sample; (2) Identify the etiology of these ARIs and ILIs; and (3) Assess individual and household factors associated with incidence and transmission of ARI/ILI. Secondary aims: (1) Assess differences in prevalence and etiology of ARI/ILI between this study's community population and those seeking acute care; and (2) Determine effectiveness of influenza vaccination on prevention of influenza illness in the study's community sample. Methods: Three hundred households will be followed for at least a year, maintaining a surveillance population of approximately 1000 individuals per year. Households will be identified by randomly sampling an existing cohort of households currently enrolled in a community-based survey study already recruited via a random, stratified sampling of households in the Washington Heights/Inwood area of Northern Manhattan. ARI/ILI surveillance will be conducted twice-weekly using text messaging with phone follow-up. Nasopharyngeal swabs will be obtained from ill household members and analyzed to identify ARI/ILI associated viruses via multiplex RT-PCR. Individual and household factors associated with ARI/ILI incidence and transmission will be assessed using general estimating equation regression models. Comparing this study's data with hospital data will assess differences in prevalence/etiology of ARI/ILI between community populations and those seeking acute care. Laboratory data will be combined with our pediatric/ adult immunization registry to determine seasonal influenza vaccine effectiveness against lab-confirmed influenza using a case-control analysis. Outcomes: The primary outcomes will be (1) incidence and prevalence of ARI/ILI; (2) etiologies of ARI/ILI; (3) factors associated with ARI/ILI incidence and transmission. Secondary outcomes will include (1) differences in the prevalence and etiology of ARI/ILI between community population and those seeking acute care; (2) influenza vaccine effectiveness in prevention of laboratory-confirmed influenza. If successful this project could provide important new information to help plan ARI/ILI interventions including new vaccines, vaccination strategies, and surveillance for viral pathogens, including future outbreaks. PUBLIC HEALTH RELEVANCE: This study will provide important information regarding the incidence, etiology and factors associated with acute respiratory illness (ARI) and influenza-like illness (ILI) in a community sample hopefully leading ultimately to better prevention and control. It will also allow a direct comparison between the etiology of viral infection in a community versus a hospital-based sample, as well as of ILI incidence in the community compared to those acutely seeking care, potentially providing important information for viral surveillance, including strategies for future outbreaks. Additionally, this project will allow the calculation of influenza vaccine effectiveness against laboratory-confirmed influenza in a community sample.